This invention relates to flashing apparatus for a geothermal power plant.
A known type geothermal power plant for generating electric power by utilizing underground hot water heated by terrestrial heat is shown in FIG. 1, in which the hot water is fed from a well 1 into a separator 2 wherein the hot water and steam are separated. The steam separated in the separator 2 is then supplied into a steam turbine 3 and the hot water remaining in the separator 2 is fed into a flashing apparatus 4. The inner pressure of the flashing apparatus 4 is lower than that of the separator 2 so as to evaporate the hot water thereby to generate steam which is additionally fed to the steam turbine to drive a generator 5. The hot water still remaining in the flashing apparatus 4 is transferred into a return well 6 and the steam used in the steam generator 3 is then condensed in a condenser 7. The condensate is mixed with cooling water and recovered in a cooling tower 9 by the operation of a pump 8.
FIG. 2 schematically shows an internal arrangement of a typical flashing apparatus of the type presently used, in which underground water heated by terrestrial heat introduced into a drum-shaped shell 11 through inlets 12 is ejected thereinto through ejecting nozzles 13. A portion of the ejected hot water is changed into flashed steam in an amount proportional to an enthalpy of the hot water to be ejected and this flashing phenomenon is enhanced by collision of the ejected hot water against guide plates 14 located near the front ends of the respective nozzles 13. The flashed steam rises in the space of the drum shell 11 and is supplied to the steam turbine through outlets 15 provided for the upper portion of the shell 11. The hot water remaining in the shell 11 is collected at the bottom thereof and then drained through a drain outlet 16 into a return pump, not shown.
With the flashing apparatus of the type as described above, after the hot water ejected from the nozzles 13 has collided against the guide plates 14, water drops each having a considerably large diameter among the water drops dispersed in the shell 11 fall by gravity and are collected at the bottom of the shell 1 as drain water. On the other hand, water drops each having a considerably small diameter rise together with flashed steam and are fed into the steam turbine 3 through the steam outlets 15.
The lower the degree of dryness of the steam caused by the mixing of the hot water drops, the higher the degree of wetness of the steam at the final operating stage of the turbine, which may cause corrosion of the nozzles and blades of the turbine. In addition, a large quantity of substances such as silica, calcium, and the like are contained in the drops of underground hot water without being separated in the flashing apparatus, so that such substances are deposited on the surfaces of the nozzles and blades located near the entrance of the turbine. Such deposited substances narrow the passages of the turbine and lower the output thereof, thus adversely affecting its operation.
As described hereinabove, in order to improve the performance and reliability of the geothermal power plant, it is necessary to obtain flashed steam including substantially no water drops of underground hot water.